So-called acyl transfer reactions involve the transfer of an acyl group (the residue of an organic acid after removal of the carboxyl hydroxy group) either internally within a chemical species or from one chemical species to another. Examples are amide formation, transesterification and hydrolysis.
It is well known that acyl transfer reactions may be catalyzed by imidazole in aqueous solution, the imidazole, which is a strong nucleophile, forming an intermediary reactive complex with the acyl group. Also polymer-supported imidazoles have been used as acyl transfer catalysts (see e.g. Skjujins, A., et al., Latv. PSR Zinat. Akad. Vestis, Kim. Ser. 1988 (6), 720-5).
It has further been shown that small peptides containing a histidine (His) residue (an amino acid which contains an imidazolyl group) may have hydrolytic activity.
Recent progress in designing structural proteins and peptides have resulted in the preparation of several peptides with substantial catalytic activity (W. F. DeGrado, Nature, 365, 488 (1993). For example, K. Johnsson et al., Nature, 365, 530 (1993) disclose a short self-associating Leu-Lys-rich helical peptide that accelerates the rate of decarboxylation by means of a Schiff's base intermediate between a substrate of oxaloacetate and an amine with an electrostatically depressed acid constant (K.sub.a). It is mentioned that the secondary structure is important for the activity.
The present invention provides improvements in designed catalytic structures including an imidazole-based catalytic function.